1. Field of the Invention
The present invention relates to an image synthesizing system for obtaining a synthesized image by synthesizing more than one divisional image which is obtained by taking photographs or radiographs of a plurality of portions of an object. The present invention is applicable, for example, to radiography of a whole spine.
2. Description of the Related Art
In various applications of radiography, an item of image data is obtained by reading a radiographic image recorded on a recording sheet or the like, and is then appropriately processed. The radiographic image is reproduced from the processed image data and recorded. The radiographic image recording and reproducing system using stimulable phosphor sheets is one of such applications. There are a number of patent applications relating to the radiographic image recording and reproducing system using stimulable phosphor sheets and being assigned to the assignee of the present application.
For example, Japanese Unexamined Patent Publication No. 3 (1991)-287248, proposes use of a long stimulable phosphor sheet having a record area corresponding to the whole length of the spine as an object of radiography so that the whole spine can be radiographed and the radiograph of the whole spine can be reproduced and recorded for diagnosis of scoliosis. However, it is not easy to handle such a long stimulable phosphor sheet, and only a dedicated reading device can read image data from such a long stimulable phosphor sheet. Therefore, Japanese Unexamined Patent Publication No. 3 (1991)-287249, proposes a radiographic image recording and reading device which uses a plurality of conventional stimulable phosphor sheets for separately radiographing a plurality of portions of an object to obtain a plurality of divisional images, and then synthesizing data of the divisional images to obtain synthesized image data representing a synthesized image for diagnosis of spinal curvature.
In addition, Japanese Unexamined Patent Publication No. 10(1998)-268451, proposes a method of separately radiographing a plurality of portions of an object to obtain divisional images, wherein an image of a reference lattice pattern is recorded in the stimulable phosphor sheets at the same time as the divisional images of the object are recorded (radiographed) therein, and a synthesized image is obtained based on the pattern. According to this method, the synthesized image is obtained so that a reference lattice pattern is reconstructed from more than one portion of the pattern included in the respective divisional images. Therefore, the synthesized image can be produced based on correct recognition of the order and orientations of the divisional images.
However, generally, the above radiographic image recording and reproducing system also handles a single radiographic image which is independent of other radiographic images handled by the radiographic image recording and reproducing system, in addition to divisional images obtained as radiographs of a plurality of portions of an object as mentioned above. Therefore, when producing a synthesized image by reading divisional images recorded in a plurality of stimulable phosphor sheets according to Japanese Unexamined Patent Publication No. 10(1998)-268451, operators must monitor correspondences between the stimulable phosphor sheets and the divisional images recorded in the respective stimulable phosphor sheets after the radiographs are obtained until the synthesizing operation is completed. Thus, a heavy load is imposed on the operators. In addition, although the operator can confirm whether or not each radiograph corresponds to one of a set of divisional images by reproducing the radiographic images on a monitor, the operation of displaying all radiographs on the monitor is very bothersome when handling a large number of radiographs.
Further, in the method according to Japanese Unexamined Patent Publication No. 10(1998)-268451, the reference lattice pattern is automatically detected, and relative positions and orientations of the divisional images are corrected based on the reference lattice pattern to obtain the synthesized image. Therefore, if the reference lattice pattern is detected incorrectly, the synthesized image cannot be obtained correctly. Furthermore, the reference lattice pattern appears as a visible image in the synthesized image, and therefore the image of the object is hard to see due to interference with the visible image of the reference lattice pattern. Otherwise, the operator may be able to perform a synthesizing operation manually without the reference lattice pattern by monitoring the divisional images on the monitor and recognizing the relative positions and orientations. However, this operation requires skill, and a heavy load is imposed on the operator.